1. Field of the Invention
The invention disclosed and claimed herein generally pertains to a method for applying a protective coating to at least one layer of a giant magneto-resistive (GMR) sensor, to inhibit corrosion. More particularly, the invention pertains to a method of the above type wherein a protective coating is applied to a layer of copper or copper alloy sandwiched between other layers of material, such as an alloy of cobalt and iron. Even more particularly, the invention pertains to a method of the above type wherein the copper and cobalt-iron layers are included in a stack of layers comprising a sensor for a read head of a magnetic media data storage system.
2. Description of the Related Art
The continuing requirement to increase storage densities of magnetic media data storage systems, such as magnetic tape drive systems, is increasing the need for more sensitive magneto-resistive sensors. Currently, anisotropic magneto-resistive (AMR) sensors are being employed in the read heads of such systems. In AMR sensors, corrosion generally has not been a significant issue associated with their use. In these sensors corrosion has been mitigated through the use of half-power storage, which keeps the sensor material warm when not in use. This, in turn, reduces the amount of corrosive gases that are adsorbed onto the sensor material. However, the maximum change in sensor resistance (ΔR/R) for an AMR sensor is only 2%. As is known by those of skill in the art, ΔR/R is a metric of total signal available from the sensor, and thus indicates the sensitivity of the sensor.
In the effort to increase data storage density in magnetic media, it has been recognized that the ΔR/R of a read sensor may be significantly increased by using a device known as a giant magneto-resistive (GMR) sensor. The ΔR/R for a GMR sensor is 10-20%. However, a major drawback associated with this type of sensor has been its increased susceptibility to corrosion. A GMR sensor generally comprises a stack of layers, wherein a central layer is formed of copper or a copper alloy. Hereinafter, for convenience, the term “Cu” is used to mean or refer to the copper or copper alloy material forming such central layer. Other layers are formed of materials such as alloys of platinum-manganese (PtMn), cobalt-iron (CoFe), nickel-iron (NiFe), ruthenium (Ru) and tantalum (Ta). The most susceptible layer to corrosion is the crucial Cu layer. The Cu layer carries substantial electric current, and the GMR effect occurs at the interface of the copper and adjoining layers, which usually are comprised of a cobalt-ferrite alloy (CoFe).
Several solutions to the Cu corrosion problem are available in the prior art. One such solution is to place a protective layer on top of the stack of sensor layers, to prevent corrosion of any of the layers. However, at least two problems exist with this solution: the protective layer can be worn off by the moving magnetic tape or other media, and the protective layer, when present, introduces spacing loss which can reduce the sensor signal and resolution to unacceptable levels.
A second prior art solution is to bury the GMR sensor within the read head of the tape drive system. This is commonly done in either a yoke structure or in a flux guide structure. However, a number of problems also arise with these solutions. Signal strength is reduced, since yoke and flux guide designs have a maximum efficiency of only 50%, with efficiency usually being closer to 20-30%. Also, the manufacture of the yoke structure tends to involve substantial complexity.
The above prior art solutions to corrosion of the Cu layer in a GMR sensor are further described hereinafter, in connection with FIGS. 3-5. It would clearly be of great benefit to provide a process for protecting the vulnerable Cu layer of a GMR sensor that did not introduce additional spacing losses between the media and the active layer of the sensor.